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2.2.2 Problems related to the presence of marine biotoxins in each country

Harmful algal blooms (HABs) are a widespread, cyclical, and economically significant problem in all OPTIMA project countries. Microalgae such as dinoflagellates and diatoms produce natural toxins that bivalves, as filter-feeding organisms, rapidly accumulate in their tissues, particularly in the digestive gland (hepatopancreas). The main syndromes are DSP (Diarrhetic Shellfish Poisoning, caused by okadaic acid from algae of the Dinophysis genus), PSP (Paralytic Shellfish Poisoning, caused by saxitoxins of the Alexandrium genus, potentially lethal to humans), and ASP (Amnesic Shellfish Poisoning, caused by domoic acid from diatoms of the Pseudo-nitzschia genus). The presence of biotoxins does not harm or kill the shellfish, but makes it temporarily unfit and highly dangerous for human consumption. Detection methods have gradually evolved from traditional (and controversial) mouse bioassays to much more precise, rapid, and safe chemical methods, such as liquid chromatography coupled to mass spectrometry (LC-MS/MS).

Current solutions, unfortunately, do not include purification (toxins are not eliminated in standard breeding facilities) and consist of temporary halts to harvesting and marketing. Work is underway on early warning systems based on hydrodynamic modeling, satellite imagery, and the presence of environmental DNA detected by sensors or oceanographic buoys. These systems can predict blooms and allow farmers to anticipate harvesting before the toxin arrives or, where possible, move their facilities to other areas or further offshore.

Analyzing the phenomenon in the five OPTIMA partner countries, specificities emerge related to oceanographic dynamics and regulatory approaches:

In Spain, the Galician mussel farming sector has historically lived with the threat of algal blooms. The spectacular upwelling dynamics (upwelling of nutrient-rich deep waters) that make the rias so productive are the same ones that, under certain wind and temperature conditions, trigger massive blooms of Dinophysis (DSP) and, less frequently but with greater alarm, of the algae responsible for PSP. The Galician monitoring system (managed by INTECMAR) is considered one of the most advanced and responsive in the world, with almost daily sampling. However, once the collection ban is triggered, it can last for months, causing losses of tens of millions of euros.

In France, the national phytoplankton and phycotoxin monitoring network (REPHY), managed by IFREMER, closely monitors over 300 points along the coast. Toxic blooms affect both Atlantic production areas (DSP and ASP) and Mediterranean basins such as the Thau Stream, where Alexandrium blooms (PSP) have previously caused prolonged shutdowns of oyster and mussel production. Here too, the economic impact for farmers is high, especially if the alerts coincide with periods of peak commercial demand.

In Italy, the problem particularly affects the coastal strip of the Middle and Upper Adriatic. The presence of okadaic acid biotoxins along the Adriatic coast is increasingly frequent: high concentrations of toxins in the phytoplankton on which bivalves feed can cause temporary closures of plants. It is increasingly common for lagoons and offshore areas where clam and mussel farming is concentrated to be subject to harvesting bans due to exceedances of DSP (often linked to Dinophysis blooms favored by eutrophication and nutrient input from the Po River) and, to a lesser extent, ASP. Local health authorities immediately close the areas as soon as legal limits are exceeded in official sampling, reopening them only after 2 consecutive compliant results within 48 h.

In Greece, the Gulf of Thermaikos, which accounts for almost all of the national mussel production, is a particularly vulnerable area. As a semi-enclosed basin, it is affected by reduced water exchange and the massive input of nutrients from agricultural sources. Here, DSP events tend to be particularly severe during spring and autumn, forcing Greek authorities to implement prolonged closures of farming areas. This pushes farmers to seek offshore areas where currents better disperse toxic phytoplankton.

In Ireland, despite having some of the cleanest waters in Europe, complex ocean currents regularly carry toxic blooms to oyster beds. Ireland is also the country where a fourth syndrome, azaspiracid poisoning (AZP), was first identified. The Irish approach is characterized by the extremely strict and rapid implementation of food safety protocols, under the auspices of the Sea Fisheries Protection Authority (SFPA). Unlike other countries that wait for the results of routine environmental sampling, Ireland has regulations mandating the immediate ban on the sale of oysters and bivalves upon the first reported case of human illness linked to their consumption (such as a norovirus outbreak, food poisoning, or suspected biotoxins). If health authorities record even a single case of infection linked to a specific oyster bed, the area is immediately closed as a precaution, pending thorough virological or toxicological investigations. This zero-tolerance approach is essential to protecting the reputation and premium brand of Irish oysters in international export markets (mainly Asia and France), but it exposes local oyster farmers to extremely high commercial risks, potentially leading to the complete closure of their farms due to sudden and unpredictable health alerts.